1. Field of the Invention
The present invention relates generally to a camera, and more particularly to a lens unit of an auto-focusing camera.
2. Description of Related Art
Over the years cameras have evolved toward lightweight and compactness; however, conventionally an auto focus structure is used for controlling the telescopic movement of a lens of the camera and the auto focus structure occupies a significant space in the camera.
The auto-focus structure of the camera focuses on an object by comparing the obtained image with the image on an image sensor. The image sensor is either a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor, and is controlled by a central processing unit (CPU) installed inside the digital camera. The lens moves back and forth around its original positions (static positions). As the lens moves, the CPU compares the image from the lens with the image in the image sensor. As the lens moves to the position where the image is the clearest, then the lens stops at the position. In this case, the lens has to be continuously driven back and forth by a motor structure. Generally the motor structure is column-shaped, including coils wound therearound and a permanent magnet being mounted around the lens. During operation of the motor, a current is applied to the coils to establish an alternating magnetic field. The magnetic field of the permanent magnet interacts with the alternating magnetic field of the coils to drive the lens to move. At the moment when the CPU detects a focused image as the lens moves back and forth, a stop signal is simultaneously sent to the motor. Therefore, the lens stops at the best focal position (static position).
To firmly secure the permanent magnet around the lens, glue is usually used. However, the glue needs a long period of time to be cured before the lens/permanent magnet combination can be assembled with other components. The long period of time needed for the glue to cure causes the manufacturing of the auto-focus lens to have a high cost and low efficiency. Such a shortcoming needs to be solved.